1. Field of the Invention
This invention relates to an electromagnetic relay, and more particularly to the contact mechanism of the electromagnetic relay.
2. Discussion of the Prior Art
U.S. Pat. No. 4,618,842 discloses a conventional electromagnetic relay.
FIG. 6 is a schematic diagram showing a cross-section of the conventional electromagnetic relay. When a electromagnet portion 1 is excited, an armature 2 is swung so as to use one end portion of card 3. As a result, the card 3 pushes an upper end portion of a movable contact piece 4 and the movable contact piece 4 is then swung so that a movable contact 5 is switched over from one stationary contact 6 to the other stationary contact 7.
Upon deenergization of the electromagnet, the movable contact piece 4 returns by its own elastic force while pushing the card 3 so that the movable contact is switched over from one stationary contact 7 to the other 6.
Recently, the electromagnetic relay is required to be made compact and small in power consumption. However, it is difficult for such relays to provide a large drive force. In order to overcome this difficulty, the conventional electromagnetic relay is so designed that its movable contact piece 4 is made small in elastic force. As a result, the movable contact piece 4 is liable to be deformed by external force. In addition, when the movable contact piece 4 is externally vibrated or subjected to an impact during its returning operation, it is liable to be returned by the inertial forces of the armature 2 and the card 3. As a result, contact bounce may occur between the movable contact 5 and the stationary contact 6, thereby shorten service life. Sometimes, the movable contact may be brought into contact with the opposite stationary contact to cause malfunctions of the electromagnetic relay.
The above-described difficulty may be eliminated by coupling a coil spring to the armature, to prevent the armature from vibrating.
However, the method has the following disadvantages. The use of a coil spring increases the number of components and the number of manufacturing steps. The coil spring cannot be combined with the armature without providing a space in the relay, which makes it difficult to miniaturize the relay.